Roberta

The birdcage witch. Her nature is rage. She continuously stamps her feet inside her cage, directing her rage at those who do not respond to her. This witch is extremely fond of alcohol, and her minions are also easy to burn.

Gotz

The birdcage witch's minion. His duty is to act with frivolous indiscretion. These birds that swarm together are idiotic men. Even though they are total good-for-nothings, they try to attract her attention by swarming around her feet and attempting to woo her. They are nothing more than objects of disgust to the witch.

Trivia and Speculation

Roberta's name may have been inspired by Roberta Knie, an American soprano well-known for her role as Brunnhilde from Wagner's Ring des Nibelungen.

The name Gotz may have been derived from Götz von Berlichingen, a German Imperial Knight and mercenary. Goethe wrote a play based on his life.

In German, there is the word "Götze" which means as much as "fake god"

Some fans think that this is the witch form of Mami Tomoe due to her headlessness, flower motif, and isolation (Roberta being trapped in a birdcage, Mami literally being alone). However, the witch's nature of "rage" combined with her association with frivolity, alcoholism, and disgust all suggest otherwise.

The theory has been disproved, as Mami's witch form has been confirmed to be Candeloro.

It's also been speculated that she may be the witch form of Kazuko Saotome, who is known to have a bad history with men and a love of alcohol. The birdcage and books in her barrier could represent the school. As Kazuko doesn't wear a ring, she probably doesn't contract in every timeline.

In Puella Magi Production Note, there is a description about her: A witch who lived for a long time as a magical girl. She is weak, as she was no longer a girl when she became a witch (mid-20s to 30s?). The form she takes in her barrier is how she would've turned out in the future (around 40s). What she desires is life. Enjoys alcohol and books.

The Guidebook states that Roberta's labyrinth design uses the concept of dolls. With the words, "I wish for friends. Friends who won't dislike me." （私の願いはお友達。私を嫌いにならないお友達）. It describes that when the Witch dies, the bird cage is getting shot down and spilling a circular rain of blood.

Roberta may have used dolls as replacement for her lack of friends, perhaps like Mami, she was alone but was unable to relate to people (or had trust issues).

Since ancient times, dolls have played a central role in magic and religious rituals, or used as representations of a deity. Dolls have also traditionally been toys for children and are also collected by adults, for their nostalgic value, beauty, historical importance or financial value.